Pigment dispersions containing dispersants prepared by controlled radical polymerization and having pendent hydrophobic polymeric segments

ABSTRACT

A pigment dispersion comprising pigment, an aqueous carrier selected from water and a mixture of water and at least one organic solvent, and a pigment dispersant is described. The pigment dispersant is prepared by controlled radical polymerization, e.g., atom transfer radical polymerization, of a radically polymerizable monomer in the presence of a polymeric initiator having at least one radically transferable group. The polymeric initiator forms the polymeric backbone segment of the pigment dispersant, and the monomer forms polymeric segments that are pendent to the polymeric backbone segment. The pigment dispersant has comb-like architecture in which the polymeric backbone segment is hydrophilic, and at least a portion of each pendent polymeric segment is hydrophobic.

FIELD OF THE INVENTION

The present invention relates to pigment dispersions containing pigment,an aqueous carrier, and a pigment dispersant prepared by the controlledradical polymerization of (i) at least one radically polymerizableethylenically unsaturated first monomer in the presence of (ii) apolymeric initiator having at least one radically transferable group.The polymeric initiator forms the polymeric backbone segment of thepigment dispersant, and the first monomer forms polymeric segmentspendent to the backbone of the dispersant. The polymeric backbonesegment of the pigment dispersant is hydrophilic, and at least a portionof each pendent polymeric segment is hydrophobic.

BACKGROUND OF THE INVENTION

Pigmented coating compositions are used in a wide variety ofapplications including, for example, corrosion resistant primers anddecorative topcoats in the automotive, industrial and appliance markets.The preparation of pigmented coating compositions generally involvesmixing binder resin(s), crosslinker(s), additives, e.g., flow additives,and solvents with a compatible pigment dispersion. Pigment dispersionsare typically prepared by mixing dry pigment with a pigment dispersantin the presence of a carrier medium, e.g., an aqueous carrier medium.

Dry pigments are available commercially in the form of agglomeratedpigment particles. Pigment agglomerates are more likely to settle out ofpigment dispersions and/or pigmented coating compositions, and areaccordingly undesirable. To break the pigment agglomerates down intosmaller agglomerates and/or individual particles generally requires theuse of energy intensive mixing means (commonly referred to as grinding),e.g., sand mills and ball mills. During the grinding process the pigmentagglomerates are broken down into smaller agglomerates and/or individualparticles the surfaces of which are wetted by the pigment dispersant.The pigment dispersant suspends or disperses the pigment particles inthe carrier medium and prevents their re-agglomeration on storage. It isdesirable that the pigment dispersion remain substantially stable, e.g.,showing minimal pigment settling and viscosity change with time, priorto its use in the preparation of a pigmented coating composition.

Reducing the environmental impact of pigmented coatings compositions, inparticular that associated with emissions into the air of volatileorganics during their use, has been an area of ongoing investigation anddevelopment in recent years. Accordingly, interest in aqueous pigmentdispersions has been increasing due, in part, to the inherently lowvolatile organic content (VOC) of the aqueous pigmented coatingsprepared therefrom, which can significantly reduce air emissions duringthe application process.

Pigment dispersants used in aqueous pigment dispersions are preferablycompatible with both the aqueous carrier medium and the hydrophobicsurfaces of the pigment particles. Such a combination of disparateproperties can be achieved with a pigment dispersant having distincthydrophobic and hydrophilic polymeric segments, i.e., having welldefined polymer chain architecture. A wide variety of radicallypolymerizable monomers, such as methacrylate and acrylate monomers, arecommercially available and can provide a wide range of propertiesincluding, for example, hydrophilic and hydrophobic properties. The useof conventional, i.e., non-living or free, radical polymerizationmethods to synthesize pigment dispersants provides little control overmolecular weight, molecular weight distribution and, in particular,polymer chain structure. Aqueous pigment dispersions containing pigmentdispersants prepared by conventional non-living radical polymerizations,typically have poor stability, e.g., the pigments re-agglomerate and/orsettle out of the dispersion, and are unsuitable for the preparation ofaqueous pigmented coatings compositions.

The continued development of aqueous pigment dispersions that are stableand suitable for the preparation of aqueous pigmented coatingcompositions is desirable. In particular, it would be desirable todevelop aqueous pigment dispersions that comprise pigment dispersantshaving well defined polymer chain architecture in which distincthydrophilic and hydrophobic polymer segments are present.

U.S. Pat. Nos. 5,807,937, 5,789,487 and 5,763,548, and InternationalPatent Publication Nos. WO 98/40415, WO 98/01480, WO 97/18247 and WO96/30421 describe a radical polymerization process referred to as atomtransfer radical polymerization (ATRP). The ATRP process is described asbeing a living radical polymerization that results in the formation of(co)polymers having predictable molecular weight and molecular weightdistribution. The ATRP process is also described as providing highlyuniform products having controlled structure (i.e., controllabletopology, composition, etc.). The '937 and '548 patents also describe(co)polymers prepared by ATRP, which are useful in a wide variety ofapplications including, for example, dispersants and surfactants.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a pigmentdispersion comprising:

(a) pigment;

(b) an aqueous carrier selected from water and a mixture of water and atleast one organic solvent; and

(c) a pigment dispersant prepared by controlled radical polymerizationof at least one radically polymerizable ethylenically unsaturated firstmonomer in the presence of a polymeric initiator having at least oneradically transferable group,

wherein said polymeric initiator forms a polymeric backbone segment, thefirst monomer forms polymeric segments pendent to said polymericbackbone segment, at least a portion of each pendent polymeric segmentis hydrophobic, and said polymeric backbone segment is hydrophilic.

The features that characterize the present invention are pointed outwith particularity in the claims which are annexed to and form a part ofthis disclosure. These and other features of the invention, itsoperating advantages and the specific objects obtained by its use willbe more fully understood from the following detailed description and theaccompanying drawings in which pigment dispersants useful in embodimentsof the invention are illustrated and described.

Other than in the operating examples, or where otherwise indicated, allnumbers or expressions referring to quantities of ingredients, reactionconditions, etc, used in the specification and claims are to beunderstood as modified in all instances by the term “about.”

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a pigment dispersant usefulin the pigment dispersions of the present invention; and

FIG. 2 is a diagrammatic representation of a pigment dispersant similarto that depicted in FIG. 1 in which the polymer chain architecture ofthe polymeric segments pendent to the polymeric backbone segment areshown in further detail.

In FIGS. 1 and 2 like reference numerals represent the same structuralsegments.

DETAILED DESCRIPTION OF THE INVENTION

Pigment dispersions according to the present invention comprise one ormore pigment dispersants which can be described generally as having acomb-like architecture, i.e., having a polymeric backbone segment withat least one polymer segment or tooth pendent therefrom. The polymericbackbone segment of the pigment dispersant is hydrophilic and at least aportion of each pendent polymeric segment is hydrophobic. Preferably, atleast the terminal portion of each pendent polymeric segment, i.e., thatportion which is furthest from the backbone, is hydrophobic. While notintending to be bound by any theory, it is believed that the hydrophobicteeth of the pigment dispersant are associated with the pigment, whilethe hydrophilic backbone is associated with the aqueous carrier of thepigment dispersion.

As used herein and in the claims, the terms “hydrophobic” and“hydrophilic” are relative to each other. The backbone segment of thepigment dispersant is hydrophilic, i.e., it is more hydrophilic than thependent polymeric segments. Correspondingly, at least a portion of eachpendent polymeric segment is hydrophobic, i.e., that portion is morehydrophobic than the backbone segment.

A more quantitative measure of the hydrophobic or hydrophilic nature ofa nonionic monomer residue can be obtained by using the followingFormula-A: 100×(oxygen weight+nitrogen weight)/(carbon weight). Monomerresidues having calculated Formula-A values of greater magnitude aregenerally considered to be more hydrophilic than monomer residues havingcalculated Formula-A values of lesser magnitude. For example, thecalculated Formula-A value is 67 for 2-hydroxyethyl methacrylate; 63 formethacrylamide; 53 for methyl methacrylate; 33 for butyl methacrylate;and 22 for 2-ethylhexyl methacrylate. Accordingly, an average Formula-Avalue can be calculated for a polymer chain segment by averaging thecalculated Formula-A values for the monomer residues within thatsegment. In an embodiment of the present invention, the hydrophilicpolymeric backbone segment of the pigment dispersant has a calculatedaverage Formula-A value of from 55 to 133, while the hydrophobic portionof each pendent polymeric segment has a calculated average Formula-Avalue of from 10 to less than 55, e.g., from 10 to 40 or from 10 to 33.The difference between the calculated Formula-A values of thehydrophilic polymeric backbone segment and the hydrophobic portion ofeach pendant polymeric segment is typically at least 10, e.g., at least25, and typically within the range of 10 to 40, inclusive of the recitedvalues.

The hydrophobic portion of each pendent polymeric segment of the pigmentdispersant typically does not contain ionic monomer residues. Thehydrophilic polymeric backbone segment of the pigment dispersant maycontain ionic monomer residues, nonionic monomer residues (e.g., havingcalculated Formula-A values of from 55 to 133) or a combination of ionicand nonionic monomer residues.

Preparation of the pigment dispersant involves the controlled radicalpolymerization of at least one radically polymerizable ethylenicallyunsaturated first monomer in the presence of a polymeric initiatorhaving at least one radically transferable group. The polymericinitiator forms the polymeric backbone segment of the pigment dispersantwhile the first monomer forms polymeric segments pendent from thebackbone, i.e., the teeth of the comb-like pigment dispersant.

As used herein and in the claims, the term “controlled radicalpolymerization,” and related terms, e.g., “living radicalpolymerization,” refers to those methods of radical polymerization thatprovide control over the molecular weight, polymer chain architectureand polydispersity of the resulting polymer. A controlled or livingradical polymerization is also described as a chain-growthpolymerization that propagates with essentially no chain transfer andessentially no chain termination. The number of living polymer chainsformed during a controlled radical polymerization is often nearly equalto the number of radically transferable groups (e.g., a multiple of thenumber of polymeric initiators and the number of radically transferablegroups per polymeric initiator) present at the beginning of thereaction. Each living polymer chain typically contains a residue of theinitiator at what is commonly referred to as its tail, and a residue ofthe radically transferable group at what is commonly referred to as itshead.

In an embodiment of the present invention, the pigment dispersant isprepared by atom transfer radical polymerization (ATRP). The ATRPprocess can be described generally as comprising: polymerizing one ormore radically polymerizable monomers in the presence of an initiationsystem; forming a polymer; and isolating the formed polymer. In thepresent invention, the initiation system comprises: a polymericinitiator having at least one radically transferable atom or group; atransition metal compound, i.e., a catalyst, which participates in areversible redox cycle with the initiator; and a ligand, whichcoordinates with the transition metal compound. The ATRP process isdescribed in further detail in international patent publication WO98/40415 and U.S. Pat. Nos. 5,807,937, 5,763,548 and 5,789,487.

Catalysts that may be used in the ATRP preparation of the pigmentdispersant, include any transition metal compound that can participatein a redox cycle with the initiator and the growing polymer chain. It ispreferred that the transition metal compound not form directcarbon-metal bonds with the polymer chain. Transition metal catalystsuseful in the present invention may be represented by the followinggeneral formula I,

TM^(n+)X_(n)  I

wherein TM is the transition metal, n is the formal charge on thetransition metal having a value of from 0 to 7, and X is a counterion orcovalently bonded component. Examples of the transition metal (TM)include, but are not limited to, Cu, Fe, Au, Ag, Hg, Pd, Pt, Co, Mn, Ru,Mo, Nb and Zn. Examples of X include, but are not limited to, halide,hydroxy, oxygen, C₁-C₆-alkoxy, cyano, cyanato, thiocyanato and azido. Apreferred transition metal is Cu(I) and X is preferably halide, e.g.,chloride. Accordingly, a preferred class of transition metal catalystsare the copper halides, e.g., Cu(I)Cl. It is also preferred that thetransition metal catalyst contain a small amount, e.g., 1 mole percent,of a redox conjugate, for example, Cu(II)Cl₂ when Cu(I)Cl is used.Additional catalysts useful in preparing the pigment dispersant aredescribed in U.S. Pat. No. 5,807,937 at column 18, lines 29 through 56.Redox conjugates are described in further detail in U.S. Pat. No.5,807,937 at column 11, line 1 through column 13, line 38.

Ligands that may be used in the ATRP preparation of the pigmentdispersant, include, but are not limited to compounds having one or morenitrogen, oxygen, phosphorus and/or sulfur atoms, which can coordinateto the transition metal catalyst compound, e.g., through sigma and/or pibonds. Classes of useful ligands, include but are not limited to:unsubstituted and substituted pyridines and bipyridines; porphyrins;cryptands; crown ethers; e.g., 18-crown-6; polyamines, e.g.,ethylenediamine; glycols, e.g., alkylene glycols, such as ethyleneglycol; carbon monoxide; and coordinating monomers, e.g., styrene,acrylonitrile and hydroxyalkyl (meth)acrylates. A preferred class ofligands are the substituted bipyridines, e.g., 4,4′-dialkyl-bipyridyls.Additional ligands that may be used in preparing pigment dispersant aredescribed in U.S. Pat. No. 5,807,937 at column 18, line 57 throughcolumn 21, line 43.

The polymeric initiator used in the preparation of the pigmentdispersant by ATRP may be selected from polyethers, polyesters,polyurethanes, polymers prepared by non-living or controlled radicalpolymerization of at least one radically polymerizable ethylenicallyunsaturated second monomer and mixtures thereof. Each polymericinitiator has at least one radically transferable group. The radicallytransferable group of the polymeric initiator may be selected from, forexample, cyano, cyanato, thiocyanato, azido, halide groups andcombinations thereof. Preferably, the radically transferable group ofthe polymeric initiator is a halide.

In the ATRP preparation of the pigment dispersant, the amounts andrelative proportions of polymeric initiator, transition metal compoundand ligand are those for which ATRP is most effectively performed. Theamount of polymeric initiator present in the reaction medium can varywidely. Typically, the weight ratio of the first monomer to thepolymeric initiator is from 0.1:1 to 10 to 1, e.g., from 0.2:1 to 1:5 orfrom 0.5:1 to 2:1.

In preparing the pigment dispersant by ATRP methods, the molar ratio oftransition metal compound to polymeric initiator is typically in therange of 10⁻⁴:1 to 10:1, for example, 0.1:1 to 5:1. The molar ratio ofligand to transition metal compound is typically within the range of0.1:1 to 100:1, for example, 0.2:1 to 10:1.

The pigment dispersant may be prepared in the absence of solvent, i.e.,by means of a bulk polymerization process. Generally, the pigmentdispersant is prepared in the presence of a solvent, typically waterand/or an organic solvent. Classes of useful organic solvents include,but are not limited to, esters of carboxylic acids, ethers, cyclicethers, C₅-C₁₀ alkanes, C₅-C₈ cycloalkanes, aromatic hydrocarbonsolvents, halogenated hydrocarbon solvents, amides, nitrites,sulfoxides, sulfones and mixtures thereof. Supercritical solvents, suchas CO₂, C₁-C₄ alkanes and fluorocarbons, may also be employed. Apreferred class of solvents are the aromatic hydrocarbon solvents,particularly preferred examples of which are toluene, xylene, and mixedaromatic solvents such as those commercially available from ExxonChemical America under the trademark SOLVESSO. Additional solvents aredescribed in further detail in U.S. Pat. No. 5,807,937 at column 21,line 44 through column 22, line 54.

The ATRP preparation of the pigment dispersant is typically conducted ata reaction temperature within the range of 25° C. to 140° C., e.g., from50° C. to 100° C., and a pressure within the range of 1 to 100atmospheres, usually at ambient pressure. The atom transfer radicalpolymerization is typically completed in less than 24 hours, e.g.,between 1 and 8 hours.

The ATRP transition metal catalyst and its associated ligand aretypically separated or removed from the pigment dispersant prior to itsuse in the pigment dispersions of the present invention. Removal of theATRP catalyst is achieved using known methods, including, for example,adding a catalyst binding agent to a mixture of the pigment dispersant,solvent and catalyst, followed by filtering. Examples of suitablecatalyst binding agents include, for example, alumina, silica, clay or acombination thereof. A mixture of the pigment dispersant, solvent andATRP catalyst may be passed through a bed of catalyst binding agent.Alternatively, the ATRP catalyst may be oxidized in situ, the oxidizedresidue of the catalyst being retained with the pigment dispersant.

The polymeric initiator forms the polymeric backbone segment of thepigment dispersant. When prepared by ATRP methods, the backbone segmentof the pigment dispersant may contain a residue of a polyether,polyester, polyurethane, or a polymer prepared by the non-living orcontrolled radical polymerization of a second monomer. As used hereinand in the claims, the term “polymeric initiator” is meant to refer topolymeric initiators, oligomeric initiators and mixtures of polymericand oligomeric initiators.

Polyethers that may be used as the polymeric initiator are prepared bymethods known to the skilled artisan. Typically, polyethers are preparedby the polymerization of one or more alkylene oxides, e.g., ethyleneoxide, propylene oxide, 1,2-butylene oxide and 2,3-butylene oxide. Thepolyether may be in the form of a homopolymer, a block copolymer (e.g.,a diblock or triblock copolymer) or a random copolymer.

The terminal hydroxy groups of the polyether may be used to introduceradically transferable groups into the polyether. For example, theterminal hydroxy groups of the polyether can be esterified ortransesterified with an alpha-halocarboxylic acid, such as2-bromopropionic acid, or an alpha-halocarboxylic acid ester, such ast-butyl 2-bromopropionate. In addition, the terminal hydroxy groups ofthe polyether may be reacted with an alpha-halocarboxylic acid halide,such as 2-bromopropionyl bromide or 2-methyl-2-bromopropionyl bromide.Examples of polyethers that may be used as polymeric initiators include,but are not limited to, 2-bromopropionate capped poly(ethylene oxide),2-bromopropionate capped poly(propylene oxide) and 2-bromopropionatecapped poly(ethylene oxide)-b-poly(propylene oxide). Polyethers usefulas polymeric initiators in the preparation of the pigment dispersant inthe present invention typically have a number average molecular weightof from 1000 to 50,000, e.g., from 3000 to 20,000, as determined by gelpermeation chromatography using polystyrene standards.

Polyesters that may be used as polymeric initiators in the preparationof the pigment dispersant may be prepared by art-recognized methods.Typically, a di-carboxylic acid functional monomer or di-carboxylic acidester functional monomer is polymerized with a diol in the presence ofan acid catalyst with the concurrent removal of water or alcohol fromthe reaction vessel. By selecting the molar ratio of carboxylic acid (orester) monomer to diol, the resulting polyester will be eithercarboxylic acid (or ester) or hydroxy terminated. To introduce branchinginto the polyester, a tri-or tetra-functional monomer, typically a triolor tertol, may be used in the polymerization in amounts less than thatwhich would result in gelation of the reaction mixture.

Classes of carboxylic acid functional monomers (and their associatedesters or anhydrides) that may be used to prepare the polyesterinitiator include, but are not limited to: linear or branched aliphaticdicarboxylic acids, e.g., oxalic acid and adipic acid; cycloaliphaticdicarboxylic acids, e.g., cyclohexane dicarboxylic acid; aromaticdicarboxylic acids, e.g., phthalic acid, isophthalic acid andterephthalic acid. Classes of hydroxy functional monomers that may beused to prepare the polyester initiator include, but are not limited to:linear or branched aliphatic diols, e.g., alkylene glycols, such asethylene glycol and propylene glycol, and poly(alkylene glycols), suchas poly(ethylene glycol); cycloaliphatic diols, e.g., cyclohexane diol;aromatic diols, e.g., catechol and resorcinol; and polyols having morethan 2 hydroxy groups, e.g., trimethylol propane, trimethylol ethane,pentaerythritol, di-trimethylol propane and di-pentaerythritol.

When the polyester is hydroxy terminated, the terminal hydroxy groupsmay be used to introduce radically transferable groups into thepolyester. The terminal hydroxy groups of the polyester may beesterified with an alpha-halocarboxylic acid, transesterified with analkyl alpha-halocarboxylic acid ester, or reacted with analpha-halocarboxylic acid halide, as described previously herein withregards to the polyether initiator. When the polyester is carboxylicacid or carboxylic acid ester terminated, esterification ortransesterification with a hydroxyalkyl alpha-bromo carboxylic acidester, such as 2-hydroxyethyl 2-bromopropionate, may be used tointroduce radically transferable groups into the polyester. Polyestersuseful as polymeric initiators in the preparation of the pigmentdispersant in the present invention typically have a number averagemolecular weight of from 1000 to 50,000, e.g., from 3000 to 20,000, asdetermined by gel permeation chromatography using polystyrene standards.

Polyurethanes that may be used as the polymeric initiator may beprepared by methods known to those of ordinary skill in the art. Suchknown methods generally involve the reaction of a diisocyanate and adiol in molar ratios that result in the formation of either anisocyanate or hydroxy terminated polyurethane. To form branchedpolyurethanes polyfunctional isocyanates, e.g., tri-isocyanates, andpolyols, e.g., triols, may be present during the polymerization inamounts that do not result in gelation of the reactants.

Classes of isocyanate functional monomers that may be used to preparethe polyurethane initiator include, but are not limited to, linear orbranched aliphatic diisocyanates, e.g., 1,4-butylene diisocyanate and1,6-hexamethylene diisocyanate; cycloaliphatic diisocyanates, e.g.,isophorone diisocyanate; aromatic diisocyanates wherein the isocyanategroups are not bonded directly to the aromatic ring, e.g., α,α′-xylenediisocyanate; aromatic polyisocyanates wherein the isocyanate groups arebonded directly to the aromatic ring, e.g., benzene diisocyanate andtoluenediisocyanate; halogenated, alkylated, alkoxylated, nitrated,carbodiimide modified, urea modified and biuret modified derivatives ofdiisocyanates belonging to these classes; and dimerized and trimerizedproducts of polyisocyanates belonging to these classes, e.g., a trimerof isophorone diisocyanate. Classes of hydroxy functional monomers thatmay be used to prepare the polyurethane initiator include, but are notlimited to, those as recited previously herein with regard to thepreparation of the polyester initiator.

When the polyurethane is hydroxy terminated, the terminal hydroxy groupsmay be used to introduce radically transferable groups into thepolyester. The terminal hydroxy groups of the polyurethane may beesterified with an alpha-halocarboxylic acid, transesterified with analkyl alpha-halocarboxylic acid ester, or reacted with analpha-halocarboxylic acid halide, as described previously herein withregard to the polyether initiator. When the polyurethane is isocyanateterminated, reaction with a hydroxyalkyl alpha-halocarboxylic acidester, such as 2-hydroxyethyl 2-bromopropionate, may be used tointroduce radically transferable groups into the polyurethane.Polyurethanes that may be used as polymeric initiators in the presentinvention typically have a number average molecular weight of from 1000to 50,000, e.g., from 3000 to 20,000, as determined by gel permeationchromatography using polystyrene standards.

In an embodiment of the present invention, the polymeric initiator is apolymer prepared from the non-living radical polymerization or thecontrolled radical polymerization of at least one radicallypolymerizable ethylenically unsaturated second monomer. The secondmonomer may be selected from vinyl monomers, e.g., (meth)acrylatemonomers, allylic monomers, olefins and mixtures thereof as will bedescribed in further detail below. As used herein and in the claims, by“(meth)acrylate” and like terms is meant methacrylates, acrylates andmixtures of methacrylates and acrylates. The term “non-living radicalpolymerization” and similar terms, e.g., “free radical polymerization,”as used herein and in the claims refer to those conventional methods ofradical polymerization that provide a lesser degree of control overpolymer chain architecture, molecular weight and polydispersity,relative to the control provided by controlled radical polymerizationmethods, such as ATRP. Non-living free radical polymerization techniquesare known to those of ordinary skill in the art, and typically make useof suitable initiators, which include organic peroxides, e.g.,di(t-butyl) peroxide, and azo type compounds, e.g.,1,1′-azobis(isobutylnitrile).

The non-living radical polymerization may optionally be performed in thepresence of chain transfer agents, such as alpha-methyl styrene dimerand tertiary dodecyl mercaptan. The non-living radical polymerization ofthe second monomer may be performed in the absence of solvent. Moretypically, the non-living radical polymerization is performed in thepresence of a solvent, most often an organic solvent, such as esters ofcarboxylic acids, ethers, cyclic ethers, C₅-C₁₀ alkanes, C₅-C₈cycloalkanes, aromatic hydrocarbon solvents, halogenated hydrocarbonsolvents, amides, nitrites, sulfoxides, sulfones and mixtures thereof.

Radically transferable groups may be introduced into the polymericinitiator during its preparation by non-living radical polymerization orby means of a post-reaction after completion of the non-living radicalpolymerization. When the polymeric initiator is prepared by non-livingradical polymerization, the radically transferable groups will typicallybe located randomly along the backbone of the prepolymer.

The introduction of radically transferable groups during the course ofthe non-living radical polymerization of the second monomer typicallyinvolves the use of radically polymerizable monomers having groups oratoms that are radically transferable under ATRP conditions. Examples ofmonomers having radically transferable groups that may be used toprepare the polymeric initiator include, but are not limited to,halomethyl styrene, e.g., p-chloromethylstyrene andp-bromomethylstyrene; alpha-halocarboxylic acid esters of hydroxyalkyl(meth)acrylates, e.g., 2-(2-bromopropionoxy)ethyl (meth)acrylate and2-(2-bromo-2-methylpropionoxy)ethyl (meth)acrylate; alpha-haloacrylates,e.g., methyl alpha-chloroacrylate; haloacrylonitriles, e.g.,chloroacrylonitrile; vinyl esters of alpha-halocarboxylic acids, e.g.,vinyl chloroacetate; allyl esters of alpha-halocarboxylic acids, e.g.,allyl chloroacetate; and mixtures of such monomers.

Radically transferable groups may be introduced into the polymericinitiator when it is prepared by non-living radical polymerization bymeans of a post-polymerization reaction. For example, residues ofhydroxyalkyl (meth)acrylates, such as 2-hydroxyalky methacrylate, in thepolymeric initiator precursor backbone may be reacted with analpha-halocarboxylic acid halide, such as 2-bromopropionyl bromide. Thepolymeric initiator prepared from the non-living radical polymerizationof at least one second monomer typically has a number average molecular(Mn) weight of from 1000 to 100,000, e.g., from 3000 to 20,000, asdetermined by gel permeation chromatography using polystyrene standards.

The polymeric initiator may also be prepared by the controlled radicalpolymerization of at least one second monomer, and can have well definedpolymer chain architecture, molecular weight and polydispersity indexvalues of less than 2.0. In an embodiment of the present invention, thepolymeric initiator is prepared by ATRP, in which case radicallytransferable groups are preferably introduced into the polymericinitiator by means of a post-polymerization reaction. For example, theATRP prepared polymeric initiator precursor may contain residues of ahydroxyalkyl (meth)acrylate, such as 2-hydroxyethyl methacrylate, inblock, alternating or gradient sequences with other monomer residues,such as methoxy poly(ethylene glycol) methacrylate. Radicallytransferable groups may then be introduced into the ATRP preparedpolymeric initiator precursor by reaction of its pendent hydroxy groupswith an alpha-halocarboxylic acid halide, such as 2-bromopropionylbromide. The polymeric initiator prepared from the controlled radicalpolymerization of at least one second monomer typically has a numberaverage molecular (Mn) weight of from 1000 to 30,000, e.g., from 3000 to20,000, and a polydispersity index (Mn/Mw) of less than 2.0, e.g., lessthan 1.8 or less than 1.5, as determined by gel permeationchromatography using polystyrene standards.

In a preferred embodiment of the present invention, the polymericinitiator is prepared from the non-living or controlled radicalpolymerization of the second monomer, and each of the first monomer(which forms the teeth of the pigment dispersant) and the second monomerare independently selected from vinyl monomers, allylic monomers,olefins and mixtures thereof. Classes of vinyl monomers from which eachof the first and second monomers may be independently selected include,but are not limited to, (meth)acrylic acid, (meth)acrylates,(meth)acrylamide, N- and N,N-disubstituted (meth)acrylamides, vinylaromatic monomers, vinyl halides and vinyl esters of carboxylic acids.

Examples of C₁-C₂₀ alkyl (meth)acrylates (including linear or branchedalkyls and cycloalkyls) from which each of the first and second monomersmay be independently selected include, but are not limited to, methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate,tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl(meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate,3,3,5-trimethylcyclohexyl (meth)acrylate and isocane (meth)acrylate.Examples of oxirane functional (meth)acrylates from which each of thefirst and second monomers may be independently selected include, but arenot limited to, glycidyl (meth)acrylate,3,4-epoxycyclohexylmethyl(meth)acrylate, and2-(3,4-epoxycyclohexyl)ethyl(meth)acrylate. Hydroxy alkyl(meth)acrylates having from 2 to 4 carbon atoms in the alkyl group fromwhich each of the first and second monomers may be independentlyselected include, but are not limited to, hydroxyethyl (meth)acrylate,hydroxypropyl (meth)acrylate and hydroxybutyl (meth)acrylate. Examplesof monomers having more than one (meth)acryloyl group, from which eachof the first and second monomers may be independently selected, include,but are not limited to (meth)acrylic anhydride, diethyleneglycolbis(meth)acrylate, 4,4′-isopropylidenediphenol bis(meth)acrylate(Bisphenol A di(meth)acrylate), alkoxylated 4,4′-isopropylidenediphenolbis(meth)acrylate, trimethylolpropane tris(meth)acrylate and alkoxylatedtrimethylolpropane tris( meth)acrylate.

Specific examples of vinyl aromatic monomers from which each of thefirst and second monomers may be selected include, but are not limitedto, styrene, p-chloromethylstyrene, divinyl benzene, vinyl naphthaleneand divinyl naphthalene. Vinyl halides from which each of the first andsecond monomers may be independently selected include, but are notlimited to, vinyl chloride and vinylidene fluoride. Vinyl esters ofcarboxylic acids from which each of the first and second monomers may beindependently selected include, but are not limited to, vinyl acetate,vinyl butyrate, vinyl 3,4-dimethoxybenzoate and vinyl benzoate.

As used herein and in the claims, by “olefin” and like terms is meantunsaturated aliphatic hydrocarbons having one or more double bonds, suchas obtained by cracking petroleum fractions. Specific examples ofolefins from which each of the first and second monomers may beindependently selected include, but are not limited to, propylene,1-butene, 1,3-butadiene, isobutylene and diisobutylene.

As used herein and in the claims, by “allylic monomer(s)” is meantmonomers containing substituted and/or unsubstituted allylicfunctionality, i.e., one or more radicals represented by the followinggeneral formula II,

H₂C═C(R₁)—CH₂—  II

wherein R₁ is hydrogen, halogen or a C₁ to C₄ alkyl group. Mostcommonly, R₁ is hydrogen or methyl and consequently general formula IIrepresents the (meth)allyl radical (i.e., the methallyl or allylradical). Examples of allylic monomers from which each of the first andsecond monomers may be independently selected include, but are notlimited to: (meth)allyl ethers, such as methyl (meth)allyl ether and(meth)allyl glycidyl ether; allyl esters of carboxylic acids, such as(meth)allyl acetate, (meth)allyl butyrate, (meth)allyl3,4-dimethoxybenzoate and (meth)allyl benzoate.

Other ethylenically unsaturated radically polymerizable monomers fromwhich each of the first and second monomers may be independentlyselected include, but are not limited to: cyclic anhydrides, e.g.,maleic anhydride, 1-cyclopentene-1,2-dicarboxylic anhydride and itaconicanhydride; esters of acids that are unsaturated but do not haveα,β-ethylenic unsaturation, e.g., methyl ester of undecylenic acid;diesters of ethylenically unsaturated dibasic acids, e.g., di(C₁-C₄alkyl)ethyl maleates; maleimide and N-substituted maleimides.

In an embodiment of the present invention, each pendent polymericsegment of the pigment dispersant contains residues of monomers selectedindependently from oxirane functional monomer reacted with a carboxylicacid selected from the group consisting of aromatic carboxylic acids,polycyclic aromatic carboxylic acids, aliphatic carboxylic acids havingfrom 6 to 20 carbon atoms and mixtures thereof; C₁-C₂₀ alkyl(meth)acrylates, e.g., including those as previously recited herein;aromatic (meth)acrylates, e.g., phenyl (meth)acrylate, p-nitrophenyl(meth)acrylate and benzyl (meth)acrylate; polycyclicaromatic(meth)acrylates, e.g., 2-naphthyl (meth)acrylate; vinyl esters ofcarboxylic acids, e.g., hexanoic acid vinyl ester and decanoic acidvinyl ester; N,N-di(C₁-C₈ alkyl) (meth)acrylamides, e.g., N,N-dimethyl(meth)acrylamide, N,N-diethyl (meth)acrylamide and N,N-dioctyl(meth)acrylamide; maleimide; N-substituted maleimides; and mixturesthereof. Examples of N-substituted maleimides include, but are notlimited to, N-(C₁-C₂₀ linear or branched alkyl) maleimides, e.g.,N-methyl maleimide, N-tertiary-butyl maleimide, N-octyl maleimide andN-icosane maleimide; N-(C₃-C₈ cycloalkyl) maleimides, e.g., N-cyclohexylmaleimide; and N-(aryl) maleimides, e.g., N-phenyl maleimide, N-(C₁-C₉linear or branched alkyl substituted phenyl) maleimide, N-benzylmaleimide and N-(C₁-C₉ linear or branched alkyl substituted benzyl)maleimide.

The oxirane functional monomer residue of the pendent polymeric segmentthat is reacted with a carboxylic acid, may be selected from, forexample, glycidyl (meth)acrylate,3,4-epoxycyclohexylmethyl(meth)acrylate,2-(3,4-epoxycyclohexyl)ethyl(meth)acrylate, allyl glycidyl ether andmixtures thereof. Examples of carboxylic acids that may be reacted withthe oxirane functional monomer or its residue include, but are notlimited to, para-nitrobenzoic acid, hexanoic acid, 2-ethyl hexanoicacid, decanoic acid, undecanoic acid and mixtures thereof.

The hydrophilic backbone segment of the pigment dispersant may containnonionic moieties, ionic moieties and combinations thereof. In anembodiment of the present invention, the hydrophilic polymeric backbonesegment contains residues of monomers selected from, for example,poly(alkylene glycol) (meth)acrylates; C₁-C₄ alkoxy poly(alkyleneglycol) (meth)acrylates; hydroxyalkyl (meth)acrylates having from 2 to 4carbon atoms in the alkyl group; N-(hydroxy C₁-C₄ alkyl)(meth)acrylamides (e.g., N-hydroxymethyl (meth)acrylamide andN-(2-hydroxyethyl) (meth)acrylamide); N,N-di-(hydroxy C₁-C₄ alkyl)(meth)acrylamides (e.g., N,N-di(2-hydroxyethyl) (meth)acrylamide);carboxylic acid functional monomers; salts of carboxylic acid functionalmonomers; amine functional monomers; salts of amine functional monomers;and mixtures thereof.

Poly(alkylene glycol) (meth)acrylates and C₁-C₄ alkoxy poly(alkyleneglycol) (meth)acrylates that may be used to prepare the hydrophilicpolymeric initiator are prepared by known methods. For example,(meth)acrylic acid or hydroxyalkyl (meth)acrylate, e.g., 2-hydroxyethyl(meth)acrylate, may be reacted with one or more alkylene oxides, e.g.,ethylene oxide, propylene oxide and butylene oxide. Alternatively, analkyl (meth)acrylate may be transesterified with a C₁-C₄ alkoxypoly(alkylene glycol), e.g., methoxy poly(ethylene glycol). Examples ofpreferred poly(alkylene glycol) (meth)acrylates and C₁-C₄ alkoxypoly(alkylene glycol) (meth)acrylates include, poly(ethylene glycol)(meth)acrylate and methoxy poly(ethylene glycol) (meth)acrylate, thepoly(ethylene glycol) moiety of each having a molecular weight of from100 to 800. An example of a commercially available C₁-C₄ alkoxypoly(alkylene glycol) (meth)acrylate is methoxy poly(ethylene glycol)550 methacrylate monomer from Sartomer Company, Inc.

Examples of carboxylic acid functional monomers that may be present asmonomer residues in the hydrophilic polymeric backbone segment of thepigment dispersant include, but are not limited to, (meth)acrylic acid,maleic acid, fumeric acid and undecylenic acid. The hydrophilic backbonesegment may contain precursors of carboxylic acid functional monomerresidues that are converted to carboxylic acid residues after completionof the polymerization, e.g., maleic anhydride and di(C₁-C₄ alkyl)maleates. For example, residues of maleic anhydride can be converted toester/acid residues or amide/acid residues by art-recognized reactionswith alcohols or primary amines, respectively. Salts of carboxylic acidfunctional monomers that may be present as monomer residues in thehydrophilic backbone include, for example, salts of (meth)acrylic acidand primary, secondary or tertiary amines, such as, butyl amine,dimethyl amine and triethyl amine.

Amine functional monomers that may be present as monomer residues in thehydrophilic polymeric backbone segment of the pigment dispersantinclude, for example, amino(C₂-C₄ alkyl) (meth)acrylates, e.g.,2-aminoethyl (meth)acrylate, 3-aminopropyl (meth)acrylate and4-aminobutyl (meth)acrylate; N-(C₁-C₄ alkyl)amino(C₂-C₄ alkyl)(meth)acrylates, e.g., N-methyl-2-aminoethyl (meth)acrylate; andN,N-di(C₁-C₄ alkyl)amino(C₂-C₄ alkyl) (meth)acrylates, e.g.,N,N-dimethyl-2-aminoethyl (meth)acrylate. The hydrophilic backbone ofthe pigment dispersant may also contain residues of salts of aminefunctional monomers, e.g., salts of those amine functional monomers asrecited previously herein. Salts of the amine functional monomerresidues may be formed by mixing a carboxylic acid, e.g., lactic acid,with the pigment dispersant after completion of polymerization.

In an embodiment of the present invention, the hydrophilic polymericbackbone segment of the pigment dispersant contains residues ofcarboxylic acid functional monomers selected from (meth)acrylic acid,maleic anhydride, maleic acid, di(C₁-C₄ alkyl) maleates, and mixturesthereof. In a still further embodiment of the present invention, thehydrophilic polymeric backbone segment of the pigment dispersantcontains residues of amine functional monomers selected from amino(C₂-C₄ alkyl) (meth)acrylates, N—(C₁-C₄ alkyl)amino(C₂-C₄ alkyl)(meth)acrylates, N,N-di(C₁-C₄ alkyl)amino(C₂-C₄ alkyl) (meth)acrylatesand mixtures thereof.

The hydrophilic polymeric backbone segment of the pigment dispersant mayalso contain cationic moieties selected from ammonium, sulphonium andphosphonium. Ammonium, sulphonium and phosphonium moieties may beintroduced into the polymeric backbone segment of the pigment dispersantby means known to the skilled artisan. For example, when the backbonesegment contains residues of N,N-dimethyl-2-aminoethyl (meth)acrylate,the N,N-dimethylamino moieties may be converted to ammonium moieties bymixing an acid, e.g., lactic acid, with the pigment dispersant.

When the polymeric backbone segment contains residues of oxiranefunctional monomers, such as glycidyl (meth)acrylate, the oxirane groupsmay be used to introduce sulphonium or phosphonium moieties into thebackbone segment. Sulphonium moieties may be introduced into thebackbone segment by reaction of the oxirane groups with thiodiethanol inthe presence of an acid, such as lactic acid. Reaction of the oxiranegroups with a phosphine, e.g., triphenyl phosphine or tributylphosphine, in the presence of an acid, such as lactic acid, results inthe introduction of phosphonium moieties into the backbone segment.

When the pigment dispersant is prepared by ATRP, it may be representedin an embodiment of the present invention by the followingrepresentative general formula III,

P—[—(M)_(s)—(G)_(p)—T]_(x)  III

in which P is the hydrophilic polymeric backbone segment, and—(M)_(s)—(G)_(p)—T is a pendent polymeric segment, at least a portion ofwhich is hydrophobic. In general formula III, G and M are different fromone another, G is a residue of at least one radically polymerizableethylenically unsaturated monomer, and residue G has moieties selectedfrom aromatic groups, polycyclic aromatic groups, aliphatic groupscontaining from 6 to 20 carbon atoms and combinations thereof. Also ingeneral formula III, M is a residue of at least one radicallypolymerizable ethylenically unsaturated monomer; and T is or is derivedfrom the radically transferable group of the polymeric initiator, whichis preferably a halide. The subscript x in general formula III is anumber from 1 to a number equal to the number of radically transferablegroups of the polymeric initiator; the subscripts p and s representaverage numbers of residues occurring in a block of residues; and p ands are each individually selected such that each pendent polymericsegment has a formula weight of at least 250.

With reference to general formula III, G may be a residue of at leastone monomer selected from (i) oxirane functional monomer reacted with acarboxylic acid selected from the group consisting of aromaticcarboxylic acids, polycyclic aromatic carboxylic acids, aliphaticcarboxylic acids having from 6 to 20 carbon atoms and mixtures thereof,(ii) alkyl (meth)acrylates having from 6 to 20 carbon atoms in the alkylgroup and (iii) mixtures of (i) and (ii). The oxirane functionalmonomer, carboxylic acids and C₆-C₂₀ alkyl (meth)acrylates may each beselected from those respective examples as recited previously herein.

With further reference to general formula III, M may be a residue of atleast one alkyl (meth)acrylate having from 1 to 4 carbon atoms in thealkyl groups. Examples of C₁-C₄ alkyl (meth)acrylates of which M may bea residue include, methyl (meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate, iso-propyl (meth)acrylate, n-butyl (meth)acrylate,iso-butyl (meth)acrylate, tert-butyl (meth)acrylate and mixturesthereof.

In an embodiment of the present invention, M is a hydrophilic residuecontaining nonionic moieties, ionic moieties and combinations thereof.In general formula III, M may be a hydrophilic residue of any of thosemonomers having nonionic moieties as described previously herein withregard to the hydrophilic backbone segment of the pigment dispersant,e.g., poly(alkylene glycol) (meth)acrylates, C₁-C₄ alkoxy poly(alkyleneglycol) (meth)acrylates and hydroxyalkyl (meth)acrylates having from 2to 4 carbon atoms in the alkyl group. Further, M may be a hydrophilicresidue of any of those monomers having ionic moieties as describedpreviously herein with regard to the hydrophilic back bone segment ofthe pigment dispersant. When M is a hydrophilic residue, the ionicmoieties it may contain include those as described previously herein,i.e., anionic moieties, such as salts of carboxylic acids, or cationicmoieties, such as ammonium, sulphonium and phosphonium.

Each of M and G in general formula III may represent one or more typesof monomer residues, while s and p represent the average total number ofM and G residues occurring per block of M residues (M-Block) and Gresidues (G-block) respectively. When containing more than one type orspecies of monomer residue, the M- and G-blocks may each have at leastone of random, block (e.g., di-block and tri-block), alternating andgradient architectures. For purposes of illustration, an M-blockcontaining 6 residues of methyl methacrylate (MMA) and 6 residues ofethyl methacrylate (EMA), for which s is 12, may have di-block,tetra-block, alternating and gradient architectures as represented ingeneral formulas IV, V, VI and VII.

Di-Block Architecture

-(MMA-MMA-MMA-MMA-MMA-MMA-EMA-EMA-EMA-EMA-EMA-EMA)-  IV

Tetra-Block Architecture

-(MMA-MMA-MMA-EMA-EMA-EMA-MMA-MMA-MMA-EMA-EMA-EMA)-  V

Alternating Architecture

-(MMA-EMA-MMA-EMA-MMA-EMA-MMA-EMA-MMA-EMA-MMA-EMA)-  VI

Gradient Architecture

-(MMA-MMA-MMA-EMA-MMA-MMA-EMA-EMA-MMA-EMA-EMA-EMA)-  VII

The G-block may be described in a manner similar to that of the M-block.

The order in which monomer residues occur along the pendent polymericsegments of the pigment dispersant is typically determined by the orderin which the corresponding monomers are fed into the vessel in which thecontrolled radical polymerization is conducted. For example, themonomers that are incorporated as residues in the M-blocks of thependent polymeric segments are generally fed into the reaction vesselprior to those monomers that are incorporated as residues in theG-blocks.

During formation of the M- and G-blocks, if more than one monomer is fedinto the reaction vessel at a time, the relative reactivities of themonomers typically determines the order in which they are incorporatedinto the living pendent polymeric segments of the pigment dispersant.Gradient sequences of monomer residues within the M- and G-blocks can beprepared by controlled radical polymerization, and in particular by ATRPmethods by (a) varying the ratio of monomers fed to the reaction mediumduring the course of the polymerization, (b) using a monomer feedcontaining monomers having different rates of polymerization, or (c) acombination of (a) and (b). Copolymers containing gradient architectureare described in further detail in U.S. Pat. No. 5,807,937 at column 29,line 29 through column 31, line 35.

Subscripts s and p represent average numbers of residues occurring inthe respective M and G blocks. Subscript s may be 0, or may have a valueof at least 1, and preferably at least 5. Subscript s also typically hasa value of less than 300, preferably less than 100, and more preferablyless than 50 (e.g., 20). The value of subscript s may range between anycombination of these values, inclusive of the recited values. Typically,subscript p has a value of at least 1, and preferably at least 5 forgeneral formula III. Also, subscript p has a value of typically lessthan 300, preferably less than 100, and more preferably less than 50(e.g., 20) for general formula III. The value of subscript p may rangebetween any combination of these values, inclusive of the recitedvalues.

In general formula III, P is a residue of the polymeric initiator, whichforms the hydrophilic polymeric backbone segment of the pigmentdispersant. As discussed previously herein, the polymeric initiator hasat least one radically transferable group, and subscript x is a numberfrom 1 to a number equal to the number of radically transferable groupsof the polymeric initiator. Subscript x may be a number from 1 to 50,e.g., a number from 1 to 20, from 1 to 10 or from 1 to 5. When x is anumber less than the total number of radically transferable groupsinitially present on the polymeric initiator, the residue of thepolymeric initiator (i.e., the polymeric backbone segment of the pigmentdispersant) will still contain a balance of radically transferablegroups bonded thereto, which are not shown in general formula III.

In general formula III, T is or is derived from the radicallytransferable group of the ATRP polymeric initiator. The residue of theradically transferable group may be (a) left on the pigment dispersant,(b) removed or (c) chemically converted to another moiety. The radicallytransferable group may be removed by substitution with a nucleophiliccompound, e.g., an alkali metal alkoxylate. When the residue of theradically transferable group is a cyano group (—CN), it can be convertedto an amide group or carboxylic acid group by methods known in the art.

In a preferred embodiment of the present invention, the radicallytransferable group is a halide, which can be removed from the pigmentdispersant by means of a mild dehalogenation reaction. The reaction istypically performed as a post-reaction after the pigment dispersant hasbeen formed, and in the presence of at least an ATRP catalyst.Preferably, the dehalogenation post-reaction is performed in thepresence of both an ATRP catalyst and its associated ligand.

The mild dehalogenation reaction is performed by contacting the halogencontaining pigment dispersant with one or more ethylenically unsaturatedcompounds, which are not readily radically polymerizable under at leasta portion of the spectrum of conditions under which atom transferradical polymerizations are performed, hereinafter referred to as“limited radically polymerizable ethylenically unsaturated compounds”(LRPEU compound).

Not intending to be bound by any theory, it is believed, based on theevidence at hand, that the reaction between the halogen containingpigment dispersant and one or more LRPEU compounds results in (1)removal of the halogen group, and (2) the addition of at least onecarbon-carbon double bond where the carbon-halogen bond is broken. Thedehalogenation reaction is typically conducted at a temperature in therange of 0° C. to 200° C., e.g., from 0° C. to 160° C., a pressure inthe range of 0.1 to 100 atmospheres, e.g., from 0.1 to 50 atmospheres.The reaction is also typically performed in less than 24 hours, e.g.,between 1 and 8 hours. While the LRPEU compound may be added in lessthan a stoichiometric amount, it is preferably added in at least astoichiometric amount relative to the moles of halogen present in thepigment dispersant. When added in excess of a stoichiometric amount, theLRPEU compound is typically present in an amount of no greater than 5mole percent, e.g., 1 to 3 mole percent, in excess of the total moles ofhalogen.

Limited radically polymerizable ethylenically unsaturated compoundsuseful for dehalogenating the pigment dispersant under mild conditionsinclude those represented by the following general formula VIII.

In general formula VIII, R₆ and R₇ can be the same or different organicgroups such as: alkyl groups having from 1 to 4 carbon atoms; arylgroups; alkoxy groups; ester groups; alkyl sulfur groups; acyloxygroups; and nitrogen-containing alkyl groups where at least one of theR₆ and R₇ groups is an organo group while the other can be an organogroup or hydrogen. For instance when one of R₆ or R₇ is an alkyl group,the other can be an alkyl, aryl, acyloxy, alkoxy, arenes,sulfur-containing alkyl group, or nitrogen-containing alkyl and/ornitrogen-containing aryl groups. The R₈ groups can be the same ordifferent groups selected from hydrogen or lower alkyl selected suchthat the reaction between the terminal halogen of the pigment dispersantand the LRPEU compound is not prevented. Also an RB group can be joinedto the R₆ and/or the R₇ groups to form a cyclic compound.

It is preferred that the LRPEU compound be free of halogen groups.Examples of suitable LRPEU compounds include, but are not limited to,1,1-dimethylethylene, 1,1-diphenylethylene, isopropenyl acetate,alpha-methyl styrene, 1,1-dialkoxy olefin and mixtures thereof.Additional examples include dimethyl itaconate and diisobutene(2,4,4-trimethyl-1-pentene).

For purposes of illustration, the reaction between the halogencontaining pigment dispersant and an LRPEU compound, e.g., alpha-methylstyrene, is summarized in the following general scheme 1.

In general scheme 1, PD-(X)_(y) represents the halogen containingpigment dispersant, and y is the number of halogens pendent from thepigment dispersant.

Upon completion of the controlled radical polymerization of thepolymeric initiator and the first monomer, the pigment dispersant has acomb-like architecture, which can be described in further detail withreference to drawing FIGS. 1 and 2. In FIG. 1, the pigment dispersant 7has a hydrophilic polymeric backbone segment 25 (which is a residue ofthe polymeric initiator), and pendent polymeric segments 28, 31 and 34(at least a portion of each being hydrophobic). Each of pendentpolymeric segments 28, 31 and 34 have a terminal group T, which is or isderived from the radically transferable group of the polymericinitiator.

When the polymeric initiator is prepared by the non-living radicalpolymerization of one or more second monomers, pigment dispersant 7 willtypically be composed of a mixture of comb-like polymers havingpolymeric backbone segments 25 of varying molecular weights and varyingnumbers of pendent polymeric segments. In addition, the second monomerresidues and the pendent polymeric residues will be distributed randomlyalong the hydrophilic polymeric backbone segment of pigment dispersant7.

In FIG. 2, the pendent polymeric segments 28, 31 and 34 of pigmentdispersant 8 are shown in further detail. Pigment dispersant 8 of FIG. 2is a diagrammatic representation of the pigment dispersant representedin general formula III, in which the polymeric backbone segment 25 isequivalent to P-, and subscript x is 3. The letters M, G, T, s and p inFIG. 2 have the same meanings as described previously herein withreference to general formula III. Each of M, G, T, s and p of pendentpolymeric segments 28, 31 and 34 of pigment dispersant 8 may be the sameor different.

Pigment dispersants useful in the pigment dispersions of the presentinvention can be described in further detail with reference to FIG. 2.In an embodiment of the present invention, the polymeric backbonesegment 25 of pigment dispersant 8 contains residues of methylmethacrylate and methoxy poly(ethylene glycol) methacrylate, M is aresidue of iso-butyl methacrylate, G is a residue of an adduct ofglycidyl methacrylate and para-nitrobenzoic acid, and s and p are eachindependently from 1 to 20. In another embodiment of the presentinvention, the polymeric backbone segment 25 of pigment dispersant 8contains residues of methyl methacrylate and methoxy poly(ethyleneglycol) methacrylate, G is a residue of an adduct of glycidylmethacrylate and para-nitrobenzoic acid, s is 0, and p is from 1 to 20.

The pigment dispersant (c) is typically present in the pigmentdispersion of the present invention in an amount of at least 0.1 percentby weight, preferably at least 0.5 percent by weight, and morepreferably at least 1 percent by weight, based on the total weight ofthe pigment dispersion. The pigment dispersant is also typically presentin the pigment dispersion in an amount of less than 65 percent byweight, preferably less than 40 percent by weight, and more preferablyless than 25 percent by weight, based on the total weight of the pigmentdispersion. The amount of pigment dispersant (c) present in the pigmentdispersion of the present invention may range between any combination ofthese values, inclusive of the recited values.

The pigment of the pigment dispersion of the present invention may beselected from inorganic pigments, such as carbon black pigments, e.g.,furnace blacks, electrically conductive carbon black pigments, extenderpigments and corrosion inhibitive pigments; organic pigments; andmixtures thereof. Examples of organic pigments that may be present inthe pigment dispersion include, but are not limited to, perylenes,phthalo green, phthalo blue, nitroso pigments, manoazo pigments, diazopigments, diazo condensation pigments, basic dye pigments, alkali bluepigments, blue lake pigments, phloxin pigments, quinacridone pigments,lake pigments of acid yellow 1 and 3, carbazole dioxazine violetpigments, alizarine lake pigments, vat pigments, phthaloxy aminepigments, carmine lake pigments, tetrachloroisoindolinone pigments andmixtures thereof. Inorganic pigments that may be present in the pigmentdispersion, include, for example, titanium dioxide, electricallyconductive titanium dioxide, and iron oxides, e.g., red iron oxide,yellow iron oxide, black iron oxide and transparent iron oxides.Extender pigments that may be present in the pigment dispersion include,but are not limited to, silicas, clays, and alkaline earth metalsulfates, such as calcium sulfate and barium sulfate. The pigmentdispersion may contain corrosion inhibitive pigments, such as aluminumphosphate and calcium modified silica.

The pigment (a) is typically present in the pigment dispersion of thepresent invention in an amount of at least 0.5 percent by weight,preferably at least 5 percent by weight, and more preferably at least 20percent by weight, based on the total weight of the pigment dispersion.The pigment is also typically present in the pigment dispersion in anamount of less than 90 percent by weight, preferably less than 80percent by weight, and more preferably less than 75 percent by weight,based on the total weight of the pigment dispersion. The amount ofpigment present in the pigment dispersion may range between anycombination of these values, inclusive of the recited values.

The pigment (a) and pigment dispersant (c) are typically togetherpresent in the pigment dispersion in an amount totaling from 20 percentby weight to 80 percent by weight, e.g., from 30 percent by weight to 70percent by weight or from 40 percent by weight to 60 percent by weight.The percent weights are based on the total combined weight of thepigment and pigment dispersant. The weight ratio of pigment (a) topigment dispersant (c) is typically from 0.1:1 to 100:1, e.g., from0.2:1 to 5:1 or from 0.5:1 to 2:1.

The pigment dispersion of the present invention also comprises anaqueous carrier selected from water and a mixture of water and at leastone organic solvent (preferably a water soluble organic solvent).Classes of organic solvents that may be present in the aqueous carrierinclude, but are not limited to, alcohols, e.g., methanol, ethanol,n-propanol, iso-propanol, n-butanol, sec-butyl alcohol, tert-butylalcohol, iso-butyl alcohol, furfuryl alcohol and tetrahydrofurfurylalcohol; ketones or ketoalcohols, e.g., acetone, methyl ethyl ketone,and diacetone alcohol; ethers, e.g., dimethyl ether and methyl ethylether; cyclic ethers, e.g., tetrahydrofuran and dioxane; esters, e.g.,ethyl acetate, ethyl lactate, ethylene carbonate and propylenecarbonate; polyhydric alcohols, e.g., ethylene glycol, diethyleneglycol, triethylene glycol, propylene glycol, tetraethylene glycol,polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol and1,2,6-hexantriol; hydroxy functional ethers of alkylene glycols, e.g.,butyl 2-hydroxyethyl ether, hexyl 2-hydroxyethyl ether, methyl2-hydroxypropyl ether and phenyl 2-hydroxypropyl ether; nitrogencontaining cyclic compounds, e.g., pyrrolidone, N-methyl-2-pyrrolidoneand 1,3-dimethyl-2-imidazolidinone; and sulfur containing compounds suchas thioglycol, dimethyl sulfoxide and tetramethylene sulfone.

When the aqueous carrier comprises a mixture of water and organicsolvent, the aqueous carrier typically contains from 30 to 95 percent byweight of water, and from 5 to 70 percent by weight of organic solvent,e.g., from 60 to 95 percent by weight of water, and from 5 to 40 percentby weight of organic solvent. The percent weights are based on the totalweight of the aqueous carrier.

The aqueous carrier (b) is typically present in the pigment dispersionof the present invention, in an amount of at least 5 percent by weight,preferably at least 15 percent by weight, and more preferably at least30 percent by weight, based on the total weight of the pigmentdispersion. The aqueous carrier is also typically present in the pigmentdispersion in an amount of less than 99.4 percent by weight, preferablyless than 80 percent by weight, and more preferably less than 60 percentby weight, based on the total weight of the pigment dispersion. Theamount of aqueous carrier present in the pigment dispersion may rangebetween any combination of these values, inclusive of the recitedvalues.

The pigment dispersion may be prepared by methods that are known tothose of ordinary skill in the art. Such known methods typically involvethe use of energy intensive mixing or grinding means, such as ball millsor media mills (e.g., sand mills), as described previously herein.

The pigment dispersion of the present invention is useful in thepreparation of, for example, coatings compositions and inks. To form apigmented coating composition, the pigment dispersion is typically mixedtogether with resins, crosslinkers, additives, such as flow controlagents, and additional solvents. Coating compositions into which thepigment dispersion of the present invention may be incorporated include,for example, liquid spray-, dip- and curtain-applied primer, basecoat(i.e., the basecoat in a color-plus-clear basecoat/clearcoat system) andtopcoat compositions, and electrodepositable coating compositions.

The present invention is more particularly described in the followingexamples, which are intended to be illustrative only, since numerousmodifications and variations therein will be apparent to those skilledin the art. Unless otherwise specified, all parts and percentages are byweight.

SYNTHESIS EXAMPLES A-D

Synthesis Examples A through D describe the preparation of a pigmentdispersant that is used to prepare a pigment dispersion according to thepresent invention as described in the pigment dispersion Example.

Example A

A polymeric initiator precursor was prepared by non-living radicalpolymerization from the ingredients enumerated in Table A. The polymericinitiator precursor was modified to form a polymeric initiator asdescribed in Example B.

TABLE A Ingredients Parts by weight Charge 1 methyl isobutyl ketone 300Charge 2 hydroxypropyl methacrylate monomer 87 methyl methacrylatemonomer 30 MPEG 550 MA monomer (a) 625 t-amylperoxy(2-ethylhexanoate)(b) 32 methyl isobutyl ketone 100 Charge 3t-amylperoxy(2-ethylhexanoate) (b) 3 methyl isobutyl ketone 20 (a) MPEG550 MA monomer is a methoxy poly(ethylene glycol) methacrylate monomerfrom Sartomer Company, Inc. (b) LUPEROX ® 575 is a free radicalinitiator obtained commercially from Elf Atochem.

Charge 1 was added to a 2 liter 4-necked flask equipped with a motordriven stainless steel stir blade, water cooled condenser, and a heatingmantle and thermometer connected through a temperature feed-back controldevice. The contents of the flask were heated to 110° C. under acontinuous dry nitrogen sweep. Charge 2 was added over a period of 2.5hours, followed by an additional 1 hour hold at 110° C. Charge 3 wasdumped into the flask, followed by a 2.5 hour hold at 110° C. Thecontents of the flask were cooled, methyl isobutyl ketone was removed byvacuum distillation, and the resin was dissolved in tetrahydrofuran to aresin solids of 64.3 percent by weight, based on total weight.

Example B

A polymeric initiator was prepared from the precursor of Example A assummarized in Table B.

TABLE B Ingredients Parts by weight Charge 1 polymeric initiatorprecursor 1206 of Example A imidazole 45 Charge 2 2-bromoisobutyrylbromide 150 Charge 3 methylene chloride 400

Charge 1 was added to a 2 liter flask equipped similarly as described inExample A. The contents of the flask were heated to 60° C., and Charge 2was added over a period of 2 hours, followed by a 4 hour hold at 60° C.Upon cooling the contents of the- flask to ambient room temperature,Charge 3 was added, the contents were then vacuum filtered throughfilter paper, and washed with 400 grams of deionized water. The filteredand washed resin was placed in a separatory funnel, from which theorganic layer was collected, dried over calcium sulfate and stripped ofsolvent by means of vacuum distillation. The stripped resin wasdissolved in toluene to a resin solids of 59.5 percent by weight, basedon total weight.

Example C

A pigment dispersant precursor was prepared by controlled radicalpolymerization from the ingredients as enumerated in the following TableC. The pigment dispersant precursor was modified to form a pigmentdispersant as described in Example D.

TABLE C Ingredients Parts by weight Charge 1 glycidyl methacrylatemonomer 80 copper powder (c) 2.8 2,2′-dipyridyl 3.5 toluene 30 Charge 2polymeric initiator of Example B (d) 400 Charge 3 magnesium silicate (e)60 (c) The copper powder had an average particle size of 25 microns, adensity of 1 gram/cm³, and was obtained commercially from OMG Americas.(d) Having a resin solids content of 59.5 percent by weight, based ontotal weight. (e) MAGNESOL synthetic magnesium silicate obtainedcommerically from The Dallas Group of America.

Charge 1 was added under to a 2 liter 4-necked flask equipped with amotor driven stainless steel stir blade, water cooled condenser, and aheating mantle and thermometer connected through a temperature feed-backcontrol device. The contents of the flask were heated to 60° C. under acontinuous nitrogen sweep. Charge 2 was added to the flask, followed bya 2.25 hour hold at 60° C. Charge 3 was then added, and the contents ofthe flask were passed through a cake of MAGNESOL synthetic magnesiumsilicate. The filtered resin was then vacuum stripped, and the solids ofthe resin was adjusted to 28.5 percent by weight, based on total weight,by the addition of methyl 2-hydroxypropyl ether.

The pigment dispersant precursor of Example C was found to have:Mn=6030; Mw=20,640; z average molecular weight (Mz)=66,600; and apolydispersity index (PDI) (i.e., Mw/Mn)=3.42.

Example D

A pigment dispersant useful in the pigment dispersions of the presentinvention was prepared from the pigment dispersant precursor of ExampleC using the ingredients as enumerated in Table D.

TABLE D Ingredients Parts by weight Polymer of Example C (f) 578para-nitrobenzoic acid 44 ethyltriphenylphosphonium iodide catalyst 0.6(f) Having a resin solids content of 28.5 percent by weight, based ontotal weight.

The ingredients listed in Table D were added to a 2 liter round bottomflask equipped with a motor driven stainless steel stir blade, watercooled reflux condenser, and a heating mantle and thermometer connectedthrough a temperature feed-back control device. The contents of theflask were heated to and held at 110° C. for 11 hours under a continuousdry nitrogen sweep. The solvent was stripped under vacuum to 61.6percent solids and the contents of the flask were then mixed withdeionized water to form an aqueous composition having a resin solidscontent of 30.3 percent by weight, based on total weight. The pH of thepolymer solution was adjusted to 8.9 with dimethylethanolamine.

Pigment Dispersion Example

A pigment dispersion according to the present invention, was preparedusing the ingredients enumerated in Table 1.

TABLE 1 Ingredients Parts by weight pigment dispersant of Example D 210defoamer (g) 2 chlorinated copper phthalocyanine 32 blue pigment (h)aqueous dimethylethanolamine (i) 0.6 deionized water 3 (g) BYK 031defoamer from Byk-Chemie. (h) B-4816 Palomar Blue chlorinated copperphthalocyanine blue pigment obtained from Bayer. (i) 50 percent byweight dimethylethanolamine in deionized water.

The pigment dispersant of Example D, defoamer and deionized water weremixed in a stainless steal beaker using a cowles blade for approximately10 minutes. The chlorinated copper phthalocyanine blue pigment was addedto the stainless steal beaker with agitation from the cowles blade. ThepH of the contents of the stainless steal beaker was adjusted to a valueof 9 by addition of the aqueous dimethylethanolamine, followed by 15minutes of additional mixing with the cowles blade to form a pre-paste.The pre-paste was then transferred to and ground in an Eiger MiniMotormill 100 (from Eiger Machine, Inc. of Chicago, Ill.). During thegrinding process, the temperature of the contents of mill did not riseabove 30° C. The pigment dispersion was removed from the mill and had apigment to pigment dispersant weight ratio of 0.5, and a solids weightof 39 percent by weight based on the total weight of the pigmentdispersion.

The pigment dispersion was found to have a mean particle size of 0.846microns (as determined using a Coulter LS 230 Particle Size Analyzerfrom Beckman Coulter Corporation), and a haze value of 13.80 percent (asdetermined using a TCS Plus Spectrophotometer Model 8870 fromByk-Gardner). Mean particle sizes of less than 2 microns and haze valuesof less than 25 percent are considered generally to be desirable foraqueous pigment dispersions of chlorinated copper phthalocyanine bluepigment having a pigment to pigment dispersant weight ratio of 0.5 and asolids content of approximately 40 percent by weight, based on totalweight.

The present invention has been described with reference to specificdetails of particular embodiments thereof. It is not intended that suchdetails be regarded as limitations upon the scope of the inventionexcept insofar as and to the extent that they are included in theaccompanying claims.

We claim:
 1. A pigment dispersion comprising: (a) pigment; (b) anaqueous carrier selected from water and a mixture of water and at leastone organic solvent; and (c) a pigment dispersant prepared by controlledradical polymerization of at least one radically polymerizableethylenically unsaturated first monomer in the presence of a polymericinitiator having at least one radically transferable group, wherein saidpolymeric initiator forms a polymeric backbone segment, the firstmonomer forms polymeric segments pendent to said polymeric backbonesegment, at least a portion of each pendent polymeric segment ishydrophobic, and said polymeric backbone segment is hydrophilic.
 2. Thepigment dispersion of claim 1 wherein said pigment dispersant isprepared by atom transfer radical polymerization; and said polymericinitiator is selected from the group consisting of polyethers,polyesters, polyurethanes, polymers prepared by non-living radicalpolymerization or controlled radical polymerization of at least oneradically polymerizable ethylenically unsaturated second monomer andmixtures thereof.
 3. The pigment dispersion of claim 2 wherein saidradically transferable group of said polymeric initiator is a halide. 4.The pigment dispersion of claim 3 wherein said polymeric initiator isprepared from the non-living radical polymerization or controlledradical polymerization of said second monomer, and each of said firstand second monomers are independently selected from vinyl monomers,allylic monomers, olefins and mixtures thereof.
 5. The pigmentdispersion of claim 4 wherein each pendent polymeric segment containsresidues of monomers selected independently from the group consistingof: oxirane functional monomer reacted with a carboxylic acid selectedfrom the group consisting of aromatic carboxylic acids,polycyclicaromatic carboxylic acids, aliphatic carboxylic acids havingfrom 6 to 20 carbon atoms and mixtures thereof; C₁-C₂₀ alkyl(meth)acrylates; aromatic (meth)acrylates; polycyclicaromatic(meth)acrylates; vinyl esters of carboxylic acids; N,N-di(C₁-C₈ alkyl)(meth)acrylamides; maleimide; N—(C₁-C₂₀ alkyl) maleimides; N—(C₃-C₈cycloalkyl) maleimides; N—(aryl) maleimides; and mixtures thereof. 6.The pigment dispersion of claim 5 wherein said oxirane functionalmonomer is selected from the group consisting of glycidyl(meth)acrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate,2-(3,4-epoxycyclohexyl)ethyl(meth)acrylate, allyl glycidyl ether andmixtures thereof; and said carboxylic acid is selected from the groupconsisting of para-nitrobenzoic acid, hexanoic acid, 2-ethyl hexanoicacid, decanoic acid, undecanoic acid and mixtures thereof.
 7. Thepigment dispersion of claim 4 wherein said hydrophilic polymericbackbone segment contains nonionic moieties, ionic moieties andcombinations thereof.
 8. The pigment dispersion of claim 7 wherein saidhydrophilic polymeric backbone segment contains residues of monomersselected from the group consisting of poly(alkylene glycol)(meth)acrylates, C₁-C₄ alkoxy poly(alkylene glycol) (meth)acrylates,hydroxyalkyl (meth)acrylates having from 2 to 4 carbon atoms in thealkyl group, N—(hydroxy C₁-C₄ alkyl) (meth)acrylamides, N,N-di-(hydroxyC₁-C₄ alkyl) (meth)acrylamides, carboxylic acid functional monomers,salts of carboxylic acid functional monomers, amine functional monomers,salts of amine functional monomers and mixtures thereof.
 9. The pigmentdispersion of claim 8 wherein the carboxylic acid functional monomersare selected from the group consisting of (meth)acrylic acid, maleicanhydride, maleic acid, di(C₁-C₄ alkyl) maleates, and mixtures thereof;and the amine functional monomers are selected from the group consistingof amino(C₂-C₄ alkyl) (meth)acrylates, N—(C₁-C₄ alkyl)amino(C₂-C₄ alkyl)(meth)acrylates, N,N-di(C₁-C₄ alkyl)amino(C₂-C₄ alkyl) (meth)acrylatesand mixtures thereof.
 10. The pigment dispersion of claim 7 wherein saidhydrophilic polymeric backbone segment contains cationic moietiesselected from ammonium, sulphonium and phosphonium.
 11. The pigmentdispersion of claim 1 wherein said hydrophilic polymeric backbonesegment of said pigment dispersant has a calculated average value of100×(oxygen weight+nitrogen weight)/carbon weight of from 55 to 133; andthe hydrophobic portion of each pendent polymeric segment of saidpigment dispersant has a calculated average value of 100×(oxygenweight+nitrogen weight)/carbon weight of from 10 to less than
 55. 12.The pigment dispersion of claim 1 wherein the weight ratio of said firstmonomer to said polymeric initiator is from 0.1:1 to 10:1.
 13. Thepigment dispersion of claim 1 wherein pigment (a) is selected frominorganic pigments, organic pigments and combinations thereof.
 14. Thepigment dispersion of claim 1 wherein pigment (a) and said pigmentdispersant (c) are together present in an amount of from 20 percent byweight to 80 percent by weight, based the total weight of said pigmentdispersion.
 15. The pigment dispersion of claim 14 wherein the weightratio of pigment (a) to said pigment dispersant (c) is from 0.1:1 to100:1.
 16. The pigment dispersion of claim 1 wherein pigment (a) ispresent in an amount of from 0.5 percent to 90 percent by weight, basedon total weight of said pigment dispersion, said aqueous carrier (b) ispresent in an amount of from 5 percent to 99.4 percent by weight, basedon total weight of said pigment dispersion, and said pigment dispersant(c) is present in an amount of from 0.1 percent to 65 percent by weight,based on total weight of said pigment dispersion.
 17. The pigmentdispersion of claim 3 wherein said pigment dispersant (c) has thefollowing representative polymer chain structure,P—[—(M)_(s)—(G)_(p)—T]_(x) wherein P is said hydrophilic polymericbackbone segment; —(M)_(s)—(G)_(p)—T is said pendent polymeric segment;G is a residue of at least one radically polymerizable ethylenicallyunsaturated monomer, said residue G having moieties selected fromaromatic groups, polycyclicaromatic groups, aliphatic groups containingfrom 6 to 20 carbon atoms and combinations thereof; M is a residue of atleast one radically polymerizable ethylenically unsaturated monomer; Gand M being different from one another; T is or is derived from saidradically transferable halide of said polymeric initiator; x is a numberfrom 1 to a number equal to the number of radically transferable halidesof said polymeric initiator; p and s represent average numbers ofresidues occurring in a block of residues; p and s are each individuallyselected such that each pendent polymeric segment has a formula weightof at least
 250. 18. The pigment dispersion of claim 17 wherein G is aresidue of at least one monomer selected from the group consisting of(i) oxirane functional monomer reacted with a carboxylic acid selectedfrom the group consisting of aromatic carboxylic acids,polycyclicaromatic carboxylic acids, aliphatic carboxylic acids havingfrom 6 to 20 carbon atoms and mixtures thereof, (ii) alkyl(meth)acrylates having from 6 to 20 carbon atoms in the alkyl group and(iii) mixtures of (i) and (ii); and M is a residue of at least one alkyl(meth)acrylate having from 1 to 4 carbon atoms in the alkyl group. 19.The pigment dispersion of claim 18 wherein said oxirane functionalmonomer is selected from the group consisting of glycidyl(meth)acrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate,2-(3,4-epoxycyclohexyl)ethyl(meth)acrylate, allyl glycidyl ether andmixtures thereof; said carboxylic acid is selected from the groupconsisting of para-nitrobenzoic acid, hexanoic acid, 2-ethyl hexanoicacid, decanoic acid, undecanoic acid and mixtures thereof; and M is aresidue of a monomer selected from the group consisting of methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate,tert-butyl (meth)acrylate and mixtures thereof.
 20. The pigmentdispersion of claim 17 wherein T is derived from a dehalogenationpost-reaction.
 21. The pigment dispersion of claim 20 wherein saiddehalogenation post-reaction comprises contacting said pigmentdispersant with a limited radically polymerizable ethylenicallyunsaturated compound.
 22. The pigment dispersion of claim 21 whereinsaid limited radically polymerizable ethylenically unsaturated compoundis selected from the group consisting of 1,1-dimethylethylene,1,1-diphenylethylene, isopropenyl acetate, alpha-methyl styrene,1,1-dialkoxy olefin and combinations thereof.
 23. The pigment dispersionof claim 22 wherein said limited radically polymerizable ethylenicallyunsaturated compound is selected from the group consisting of1,1-diphenylethylene, alpha-methyl styrene and combinations thereof. 24.The pigment dispersion of claim 23 wherein s is from 0 to 20, and p isfrom 1 to
 20. 25. The pigment dispersion of claim 17 wherein M is ahydrophilic residue containing nonionic moieties, ionic moieties andcombinations thereof.